The winner of the Best Illusion of the Year contest goes to Christopher D. Blair, Gideon P. Caplovitz, and Ryan E.B. Mruczek of the University of Nevada for an animated version of the Ebbinghaus illusion.
The classic Ebbinghaus is an illusion of relative size perception in which two identical circles are placed near to each other with one surrounded by large circles and the other surrounded by small circles. The size difference between the surrounding circles causes the center circles to appear to be different sizes.
The new version referred to as the Dynamic Ebbinghaus, takes the classic static illusion and turns it into a moving display where the central circle stays the same but the surrounding circles continually grow and shrink.
Here's a video showcasing the development of the illusion.